Use Terms "Pubkey Script" And "Signature Script"

This modifies commits provided by @petertodd to use the terms "pubkey
script" and "signature script" instead of other terms.

* Rename "scriptPubKey" and "output script" to "pubkey script"
  (suggested by @luke-jr). We leave a token "scriptPubKey" at the point
  where we define pubkey script so that searchers can find it.

* Rename "scriptSig" to "signature script" (suggested by @luke-jr). We
  also leave a token "scriptSig" at this definition point.

* Rename "redeemScript" to "redeem script"

* Defined ECDSA on secp256k1 curve as the crypto used in the Transaction
  section and added references to secp256k1 private/public keys and
  signatures.

* Removed "The Parts Of A Transaction" illustration by commenting it out
  in the HTML. Shoehorning the pubkey/signature script terms into this
  image was becoming difficult, and I'm not very fond of that
  illustration anyway. I'll see if I can think of a nicer replacement
  illustration for some point in the future.

* Add a short paraphrased version @petertodd's description of scripts as
  generalized crypto.

* Updated all the illustrations which referred to either pubkey scripts
  or signature scripts to use these terms.

_autocrossref.yaml

@@ -144,8 +144,12 @@ proof of work:
 proof-of-work: proof of work
 protocol buffer: protobuf
 protocol buffers: protobuf
+pubkey: public key
 pubkey hash:
 pubkey hashes: pubkey hash
+pubkey script:
+pubkey scripts: pubkey script
+pubkeys: public key
 public key:
 public keys: public key
 public key infrastructure: pki
@@ -154,7 +158,7 @@ raw format:
 rawtransaction format: raw format
 receipt:
 recurrent rebilling:
-redeemScript:
+redeem script:
 refund: 
 refunds: refund
 regression test mode:
@@ -165,12 +169,8 @@ RPCs: rpc
 RPC:
 satoshi:
 satoshis: satoshi
-scriptPubKey:
 '`script`': pp script
 script hash:
-scriptPubKeys: scriptPubKey
-scriptSig:
-scriptSigs: scriptSig
 secp256k1:
 sequence number:
 sequence numbers: sequence number
@@ -183,6 +183,8 @@ SIGHASH: signature hash
 '`SIGHASH_SINGLE|SIGHASH_ANYONECANPAY`': shs_shacp
 signature:
 signature hash:
+signature script:
+signature scripts: signature script
 signatures: signature
 SPV:
 stack: